Covalent bonding happens between atoms with similar electronegativity, which is defined as...
a chemical property that describes the tendency of an atom or a functional group to attract electrons (or electron density) towards itself. An atom's electronegativity is affected by both its atomic number and the distance that its valence electrons reside from the charged nucleus. The higher the associated electronegativity number, the more an element or compound attracts electrons towards itClick here for a fancy periodic table of the electronegativities of the elements. As a note, you don't need to know much more about electronegativity at this point...but it is interesting!
Electronegativity determines what is polar and non-polar (which you might remember from solubility - like dissolves like, so polar solvents dissolve polar solutes and non-polar solvents dissolve non-polar solutes.)
As an aside, oils are considered non-polar, which is why water and oil don't mix, and we can't put oil soluble things into water and vice versa. They won't mix because the polarity is different!
Covalent bonding is the type of bonding that leads to single, double, and triple bonds, like those found in a lot of our ingredients. For instance, with oils, when we have a saturated oil, this means it only has single bonds. Double and triple bonds lead to unsaturated oils! (Click here for the emollients section and read the chemistry of oils part! There's a lot there, and we will be reviewing this shortly!)
Ellbie described the difference between ionic bonding and covalent bonding like this...
Ionic bonding is like a couple living together, you are very happy at the moment but if another attractive ion comes along, with the right charge, then it is like I'm outta here, baby. On the other hand covalent bonding is more like marriage, it takes energy (ie. guns, lawyers,or money) to break that bond.
I love this description!
Join me tomorrow for a little more information on chemistry as we continue to look at essential oils.